Chirotherium sp. – Deposits

Rob Hope (France)

For a few years, a large number of Permian fossil footprints have been discovered within the pink mudstone horizons of France’s Lodéve basin (Fig. 1). I’ve spent a while researching the fossils of this barren area, together with studying from papers written by an array of specialists, in addition to visiting museum and college collections of fossils from the realm. My self-appointed investigation ultimately took me to an obscure and overgrown uranium quarry within the coronary heart of the Lodévian badlands. There, I found in situ footprint fossils, and rocks showing ripple marks as well as the traces of ancient Permian raindrops.

Later, while researching the Lodéve region further still, I came across yet more palaeontological papers concerning a later geological time – that of the Anisian stage of the Middle Triassic (240 million years ago). And, once again, the dark mudstone fossils from this particular sequence include enigmatic fossil footprints. There are for example traces of Rotodactylus sp., which some authors have described as the trails of a primitive dinosaurian.

In addition, the distinctive trace fossil, Chirotherium sp. has also been found. Fossil prints from this Triassic ichnospecies (that is, categories of morphologically distinctive trace fossils)have been excavated throughout the world and were first described in 1835, by J Kaup. During the hundred years following their initial discovery, they caused heated debate within academic society, because the pes and manus prints from this prehistoric animal look somewhat like a human hand.

German palaeontologist, Wolfgang Soergel, suggested that the Chirotherium trail fossils originated from a crocodilian-type creature, and possible ancestor of a dinosaur linage. In 1925, he thought that the thumb-like appendix was simply an underdeveloped, exterior fifth finger.

Forty years later, the fossil remains of a large prehistoric animal were uncovered by excavator B Krebs within Mid-Triassic sediments of Switzerland. The foot morphology from this specimen fitted precisely with the strange Chirotherium fossil trails, proving Soergel’s exterior-thumb description to be correct. This Chirotherium-type pseudosuchian reptile is known as Ticinosuchus ferox. (However, they are now considered to be non-dinosaurian. For more on this reptile and Chirotherium generally, see Stephan Lautenschlager’s and Dr Julia Brenda Desojo’s article It doesn’t always have to be dinosaurs – a short review of rauisuchian archosaurs.)

Despite the fact that the older, red-coloured Permian reminders of Lodéve give a wonderful insight of a rich and bustling waterhole-in-big-desert environment, the footprint fossils here tend to be small, if not tiny. In fact, they are scuffed and in a somewhat friable condition. From the point of view of quality, it is the Triassic mega-track fossils (see Fig. 2) that win the day at this vast and rich site.

A scientific study, undertaken by G Gand and colleagues in 1987, has correlated the entire Permian/Triassic tetrapod ichnofauna from within this fantastic basin, and lists a total of 22 ichnospecies. The fossil assembly here was first examined in 1857 by the French naturalist, P Gervais. 

The photograph shows a big Lodévean slab, which is part of the Guimet Natural History Museum collection in Lyon. It holds numerous Rhynchosaurus prints (these are frequently used by scientists as Mid-Triassic biostratigraphic indicators), and, on the far right of the photograph, is a superb, single Chirotherium cast.